Method and apparatus for degassing liquid steel

ABSTRACT

A method of and device for degasifying liquid steel batch by batch by vacuum treatment in a gas extraction chamber filled with a suction intake pipe extending down into a ladle containing the liquid steel to be degasified, according to which while holding said ladle and said gas extraction chamber stationary, displacing a batch of molten steel from said ladle into said degasifying gas extraction chamber, degasifying said last-mentioned batch in said gas extraction chamber and releasing the degasified batch from said chamber.

United States Patent Inventor Appl. No.

Filed Patented Assignee Priority METHOD AND APPARATUS FOR DEGASSINGPrimary Examiner-Donald R. Schran Allorney-Walter Becker ABSTRACT: Amethod of and device for degasifying liquid .steel batch by batch byvacuum treatment in a gas extraction chamber filled with a suctionintake pipe extending down into ggfik n s a ladle containing the liquidsteel to be degasified, according g g to which while holding said ladleand said gas extraction US. Cl 266/34 V chamber stationary, displacing abatch of molten steel from Int. Cl

2l 7/10 said ladle into said degasifying gas extraction chamber, degasi-Field of Search 26 /3 34 fying said last-mentioned batch in said gasextraction chamber V and releasing the degasified batch from saidchamber.

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SHEET 1 OF 3 INVENTOR: Waar Mar/a,

PATENTEDunv 9 1971 saw 2 OF 3 INVENTOR. 7 0 0 Mil/4r) BY the barometriccolumn METHOD AND APPARATUS FOR DEGASSING LIQUID STEEL The presentinvention relates to a method of and a device for the removal of gasfrom liquid steel, batch by batch, by vacuum treatment in a gasextraction chamber fitted with a suction intake pipe extending down intoa ladle.

For the removal of gas from a batch at atime, steel, tapped ofl into anordinary ladle, through a suction pipe partially exhausted gas Themolten steel rises the pressure difference tion chamber and the theliquid is conveyed in batches, extending down into the ladle, into aextraction chamber situated above it. initially in the suction pipebecause of between the vacuum within the extracatmosphere over the bathin the ladle, of liquid steel usually attaining a height of about 1.4meters. To remove the gas from the steel, either the extraction chamberor a ladle is raised and lowered, for example, by means of hydraulicequipment. As the extraction chamber is lowered or the ladle is raised,part of the molten steel rises into the extraction chamber, in which ityields up its gas. When the extraction chamber is raised or the ladle islowered, this batch of steel, now freed from gas, flows back into theladle. This process is repeated until the requisite degree of degassinghas been achieved throughout the entire charge of steel.

in the method just described, for the removal of gas from molten steelin small batches, a great deal of power is needed for imparting relativemotion to the refractory-lined gas extraction chamber, with theequipment mounted on it for the admission of fluxes and so forth, and tothe ladle mechanism its entire charge of molten metal, all of whichrepresent a very considerable deadweight. The moving mechanism, which isnecessarily very robust because of the heavy nature of steelmaking work,is highly expensive and bulky.

Dust and heat reduce the life of this mechanism and give rise to heavymaintenance costs.

It is, therefore, an object of this invention to provide a method of anddevice for degasifying liquid steel, which will overcome theabove-mentioned drawbacks.

It is another object of this invention to provide amethod of and devicefor batchwise removing gas from liquid steel by vacuum treatment,according to which it is no longer necessary to more the gas extractionchamber and the ladle in relation to each other while the gas is beingremoved.

These and other objects and advantages of the invention will appear moreclearly from the following specification, in connection with theaccompanying drawing, in which:

FIG. l diagrammatically shows a gas removal device according to theinvention, in vertical section, with the displacement vessel securednoncoaxially to the gas extraction chamber;

FIG. 2 shows in vertical section a gas extraction chamber according tothe invention, with the displacement chamber flanged onto the gasextraction chamber coaxially with the intake pipe thereof;

FIG. 3 illustrates in vertical section a gas extraction chamberaccording to the invention with flange-attached cover, to provide apressuretight closure on the ladle containing the charge of moltensteel.

Taking as its starting point the existing methods whereby gas is removedfrom liquid steel by..the vacuum treatment of small batches in anextraction chamber fitted with a suction intake pipe extending down intothe ladle, the invention achieves its purpose by virtue of the fact thatthe batches of molten metal are expelled from the ladle pneumatically ormechanically and thus raised into a gas extraction chamber situatedabove the ladle.

The particular advantage of the method here proposed lies in the factthat the only power it is now necessary to expend is that which isrequired to raise the sum of all the batches of molten metal. Thisadvantage can best be demonstrated by the following numerical example.For adequately degassing 100 tons of molten steel, the method usedhitherto entails raising the gas extraction chamber, which itself weighsapproximately gas, is admitted, the molten suretight cover fitted with40 tons, about 30 times. Making allowance in the calculation for acirculation factor of 3, the amount of steel treated in each instance inthe gas extraction chamber is only (3Xl00)/3 =10 tons. Hence, if allthat is lifted at each stroke is the batch of metal being degassed,instead of the extraction chamber itself, this makes a difference inweight of about 30 tons of each stroke.

in one advantageous fonn of equipment for putting the invention methodinto practice, a bell-type displacement vessel, open at the bottom andfitted at the top with a pressure feedpipe and a pressure relief pipe",extends down into the charge in the ladle, adjacent to the intake pipeof the gas extraction chamber. When this is used, it has been founddesirable to connect the displacement vessel rigidly to the gasextraction chamber. When a fluid under pressure, such as air or an inertsteel inside the displacement vessel is expelled, with the result thatthe level of the melt rises correspondingly in the ladle and in the gasextraction chamber. When the pressure in the displacement vessel isrelieved, the melt flows back into the ladle again.

In another form of equipment, the molten steel is expelled from theladle by a bell chamber lowered into the charge and raised from it bymechanical means.

In yet another form of equipment, the displacement vessel can be madecoaxial with the extraction chamber intake pipe and flanged on to theextraction chamber along with this pipe.

in another advantageous arrangement for putting the invention methodinto practice, the ladle is provided with a prespressure feed andpressure relief pipes, the extraction chamber intake pipe extending downthrough the cover, into which it is sealed, into the molten charge.

With all three forms of equipment for putting the invention method intopractice, the gas extraction chamber and the displacement vessel orcover should preferably be stationary, while the'ladle containing thecharge of molten steel is raised once only from below to the appropriateheight. Alternatively,

' it is possible for the extraction chamber, complete with displacementvessel and/or cover, to be mounted from above and secured to the chargedladle, this bring stationary.

- Referring now to the drawings in detail, and FIG. 1 thereof inparticular, the equipment shown therein comprises a ladle 10 of standardtype fitted with a stopper lifting rod 11, said ladle containing thecharge of molten metal 12. Above the ladle 10 is a gas extractionchamber 13. At the top of the extraction chamber 13 is a dome 14,carrying a connection flange 15 for the vacuum pump connection or thelike (not shown). Near the top or about halfway up, the extractionchamber 13 has a charging pipe 16 directed obliquely downwards andhaving mounted thereon a device 17 for gauging the charges of whateveradditional materials are to be introduced. The base of the extractionchamber 13 carries a pipe stub 18, to provide a pressuretight connectionfor the intake pipe 19.

The displacement vessel 22, which is open at the bottom, is securedeccentrically to the gas extraction chamber 13 by means of the anchorage2!. The top end of the displacement vessel is fitted with a pressurefeedpipe 23 and a pressure relief pipe 24 with shutofi valves 25.

While the intake pipe 19 extends only a short way down into the moltensteel 12, the displacement vessel 22 dips far more deeply into thesteel. By the introduction of fluid under pressure into the'displacementvessel 22, the'molten metal in said vessel 22 can be lowered from itsassumed level a to the level 1:, the level in the ladle thereby becomingadjusted to b. At the same time, the level of the steel within the gasextraction chamber 13, which at 0 corresponds to the vacuum P, will riseto the extent of h, the new level in the gas extraction chamber 13 nowbeing b". As soon as the pressure fluid is allowed to escape from thedisplacement vessel 22 through the pressure relief pipe 24, the twolevels of the steel, b and b", will drop again to the correspondinglevels a and a. By virtue of the fluid being repeatedly pumped into andreleased from the displacement vessel 22, the entire charge of moltensteel will be forced in successive batches into the gas extractionchamber 13, where its gas will be removed.

In the example shown in FIG. 2, the displacement vessel 32 is mountedcoaxially about the intake pipe 19. The displacement vessel, along withthe pipe 19, is by means of a pipe connection 33 flanged onto the pipeconnection 18 of the gas extraction chamber 13. The rising and fall ofthe batches of metal is also in this instance effected in the mannerdescribed in connection with FIG. 1 by means of a fluid pumped into thedisplacement vessel 32 under pressure, which fluid is subsequentlyreleased.

in the example illustrated in FIG. 3, a cover 42 to provide apressuretight closure on the ladle 10, is secured by the pipe connection43 to the pipe connection 18 on the gas extraction chamber 13. [n thisarrangement, after the tapping and charging of the molten steel 12, theladle 10 is raised and forced up under the cover 42 to form apressuretight seal with the aid of an interposed packing 44, which maybe water cooled. It is also possible, of course, for the cover, alongwith the complete gas extraction chamber and intake pipe, to be placedupon the ladle and pressure tightly fitted thereon.

The raising of the batches of metal from the charge 12 into the gasextraction chamber 13 and their return to the ladle are in conformitywith FIG. 3 effected by the admission of fluid under pressure to thecontainer formed by the ladle l and its cover 42, following by releaseof the fluid. As the fluid is forced in, the level a of all the metal inthe ladle will drop to b. In this example, the difference in level hwithin the gas ex traction chamber 13 now depends solely on thegeometrical dimensions of the gas extraction chamber 13 and on thevolume of steel expelled from the ladle l0.

It is, of course, to be understood that the present invention is notlimited to the specific showing in the drawings but also comprises anymodifications within the scope of the appended claims.

What I claim is:

l. A device for degasifying liquid steel batch by batch whereby part ofmolten steel is lifted by pneumatic displacement from a vessel into adegasifier vessel, which includes: a first vessel adapted to receive andhold a charge of molten steel to be degasified, gas extraction chambermeans arranged above said first vessel and provided with downwardlyextending tubular means extending into said first vessel, and a belltypedisplacement vessel closed at the top and open at the bottom andextending downwardly into said first vessel and fed at its upper portionwith a feedpipe for selectively conveying pressure fluid into saidbell-type displacement vessel to displace a batch of molten metal fromsaid first vessel into said gas-extracting chamber, the upper portion ofsaid displacement vessel also being provided with an adjacent exhaustpipe for releasing pressure fluid from said displacement vessel torelease the degasified batch from said extraction chamber means.

2. A device according to claim 1, in which said displacement vessel isconnected rigidly to said gas extraction chamber means.

3. A device according to claim 1, in which said displacement vessel ismounted coaxially about said downwardly extending tubular means and isflanged onto said gas extraction chamber means together with saiddownwardly extending tubular means.

2. A device according to claim 1, in which said displacement vessel isconnected rigidly to said gas extraction chamber means.
 3. A deviceaccording to claim 1, in which said displacement vessel is mountedcoaxially about said downwardly extending tubular means and is flangedonto said gas extraction chamber means together with said downwardlyextending tubular means.